1. Field of the Invention
The invention relates to a hydraulic damper for an electromechanical valve, and in particular, to a hydraulic damper that can provide relatively soft seating of an engine valve on an engine valve seat.
2. Background Art
Internal combustion engines have been designed that utilize electromechanically actuated intake and exhaust valves. Known electromechanical valves use first and second solenoids to induce an inner armature to move in first and second axial directions, respectively. The armature may be coupled to a valve member that opens and closes a respective port to an engine cylinder. A problem associated with known electromechanical valves is that it is extremely difficult to control the landing speed (i.e., the seating speed) of a valve head against a valve seat. If the landing speed is too high, the engine valve seat can become degraded.
In an attempt to solve this problem, a known system in U.S. Pat. No. 5,832,883 utilized a hydraulic damper for reducing the seating speed in an electromechanical valve assembly. In this damper system, a piston is disposed in a chamber filled with oil. The piston is connected to a valve member and separates the chamber into an upper portion and a lower portion. The piston also contains a constant area orifice extending therethrough. The first and second chamber portions are also connected by a conduit. As the piston moves in a first direction, fluid is pushed through the conduit (and the constant area orifice) from the first chamber portion to the second chamber portion. When the piston moves proximate an end position and closes off an opening to the conduit, the constant area orifice continues to allow fluid to pass from the first chamber portion to the second chamber portion. The fluid flow through the constant area orifice, however, prevents the damping pressure in the first chamber from reaching a relatively high pressure. Further, the reduced damping pressure in the first chamber portion can result in the valve memberxe2x80x94connected to the damper pistonxe2x80x94having a relatively high seating speed when it contacts the valve seat. As discussed above, the relatively high landing speed may undesirably degrade the valve seat and valve member.
Another known hydraulic damper is described in U.S. Pat. No. 6,205,964. The hydraulic damper includes a damping piston that only contacts a valve member near a valve seating position. However, a problem with this damper is that intermittently contacting of the valve member against a damper piston can generate undesirable noise.
Thus, the inventors herein have recognized that a hydraulic damper for electromechanical valve assemblies is needed that can reduce and/or eliminate one or more of the above-mentioned deficiencies.
A hydraulic system in accordance with the present invention provides relatively soft seating for a valve member on an engine valve seat.
The hydraulic system for an electromechanical valve includes a housing defining a chamber for holding fluid extending along an axis. The system further includes a damper stem disposed in the chamber configured to move along the axis. The damper stem is configured to be directly coupled to a valve member. The system further includes a piston coupled to the damper stem dividing the chamber into a first chamber portion and a second chamber portion. The housing includes a conduit extending between the first chamber portion and the second chamber portion. The conduit has a first non-cylindrical opening communicating with the first chamber portion. When the piston moves past at least a portion of the non-cylinder opening, the cross-sectional area of the opening decreases to restrict fluid flow from the first chamber to reduce a velocity of the piston. The area of this opening continues to decrease as the valve approaches its seat.
The hydraulic system in accordance with the present invention provides a substantial advantage over known systems. In particular, the hydraulic system utilizes a conduit having a non-cylindrical opening to control a damping force prior to and during valve seating to dramatically reduce a seating velocity.
Another advantage of the present system is that the damper stem of the damper can be directly coupled to an engine valve member to remove any undesirable contact noise between a valve member and a component of the damper.